Caption: Barrett's oesophagus, gross specimen. This is a condition that affects the part of the oesophagus (left) that adjoins the stomach (right). The cells lining the lower oesophagus, characterized by a normally smooth mucosal surface, change into cells similar to those which line the stomach, a type of change known as dysplasia. The region of dysplasia in this case is the brown area at the centre. It often results from prolonged gastric reflux (heartburn), where stomach acid has frequently entered the oesophagus. There is a risk that the dysplastic tissues may develop into cancer, and therefore requires frequent monitoring.